WDPN32 PGTW 150300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (ATSANI) WARNING NR 04// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 17W (ATSANI), LOCATED APPROXIMATELY 187 NM NORTH OF ENEWETAK, HAS TRACKED WESTWARD AT 02 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY-EXPOSED, WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH MULTIPLE CONVECTIVE BANDS WRAPPING INTO THE CENTER. HOWEVER, MSI INDICATES VERY SLOW TRACK MOTION, PERHAPS QUASI-STATIONARY MOTION, OVER THE PAST SIX HOURS. OVERALL, THERE IS GOOD CONFIDENCE IN THE CURRENT POSITION. A 142105Z SSMIS 37 GHZ IMAGE REVEALS IMPROVED CONVECTIVE STRUCTURE WITH TIGHTLY-CURVED BANDING WRAPPING INTO THE CENTER. DESPITE THE CONSOLIDATING LLCC, THE DVORAK ESTIMATES REMAIN AT T2.5 (35 KNOTS), THEREFORE, THE CURRENT INTENSITY REMAINS ASSESSED AT 35 KNOTS, WHICH IS SUPPORTED BY A 142222Z ASCAT IMAGE SHOWING AN EXPANSIVE AREA OF 30 TO 35 KNOT WINDS. TS 17W IS EMBEDDED WITHIN A COMPETING STEERING ENVIRONMENT BETWEEN A SUBTROPICAL RIDGE (STR) TO THE NORTH AND A NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTH. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. AS REFLECTED IN THE BULK OF DYNAMIC MODEL GUIDANCE, SLOW, QUASI-STATIONARY TRACK MOTION IS FORECAST OVER THE NEXT 36 HOURS AS THE SYSTEM REMAINS IN A COMPETING STEERING ENVIRONMENT. AFTER TAU 36, THE NER IS FORECAST TO WEAKEN AND SHIFT EASTWARD ALLOWING THE STR TO BUILD AND BECOME THE DOMINANT STEERING INFLUENCE. THIS WILL ALLOW TS 17W TO ACCELERATE WEST-NORTHWESTWARD TO NORTHWESTWARD THROUGH TAU 72. TS 17W IS EXPECTED TO RAPIDLY INTENSIFY AFTER TAU 24 UNDER VERY FAVORABLE ENVIRONMENTAL CONDITIONS TO INCLUDE RADIAL OUTFLOW, WARM SST AND HIGH OCEAN HEAT CONTENT. C. IN THE EXTENDED TAUS, TS 17W WILL MAINTAIN A NORTHWESTWARD TRAJECTORY AS THE SYSTEM TRACKS ALONG THE WESTERN PERIPHERY OF THE STR. AVAILABLE MODEL GUIDANCE REMAINS IN GOOD AGREEMENT, HOWEVER, THERE IS LOW OVERALL CONFIDENCE IN THE FORECAST TRACK DUE TO THE ERRATIC MOTION EXPECTED IN THE SHORT-TERM.// NNNN